Molding compositions



Patented Mar. 11, 1952 MQLDING COMPO SIIIONS ration of Delaware NDrawing. Application March 31, 1950, Serial No. 153,301

This invention concerns new molding compositions comprisingthermoplastic monovinyl aromatic resins together with certain agents forproducing a nacreousor mother-of-pearl appearance. It pertainsmoreparticularly' to molding compositions comprised essentially'ofpolystyrene and a polyethylene glycol and relates to a method of makingthe same.

It is known to incorporate a polyalkylene oxide or a polyalkylene glycolwith polystyrene resins as mold release agents or lubricants. It hasbeen proposed that an amount of the polyalkylene glycol corresponding toone per cent by weight or less of the resin is suificient to providesatisfactory improvement in the release properties without producing adeleterious eiiect on other characteristics of the resin, e. g. lightstability or water absorption. The polyalkylene glycols are usuallyemployed as mold release agents in amounts such that the glycols arecompletely soluble in the solidresins so as to avoid the formation ofopaque or translucent moldings.

It has now been found that when polyethylene glycols are intimatelyincorporated with thermoplastic monovinyl aromatic resins, e. g.polystyrene, in amounts greater than the solubility of the polyalkyleneglycol in the solid resin that the resulting compositions can be moldedby 5'Glaims. (Cl.26033.2)

. copolymers of monovinyl aromatic compounds desired molecular weight.

usual injection molding operations to form articles which possess anacreous or mother-of-pearl appearance. It has further been found thatthe the compositions when molded, particularly by injection moldingoperations, form articles which also possess excellent elongation andimpact strength and are resistant to breakage by flexmg.

Accordingly, the invention comprises molding compositions consistingprincipally of a thermoplastic monovinyl aromatic resin, preferablypolystyrene, having intimately incorporated therewith a polyethyleneglycol in amount exceeding the solubility of the polyethylene glycol inthe solid polymer, which compositions can be molded by usual compressionor injection molding operations to form articles having an opaque,nacreous, or mother-of-pearl appearance, together with improved impactstrength and elongation.

Polystyrene is the preferred monovinyl aromatic polymer, although theresinous thermoplastic polymers and copolymers of other monovinylaromatic compounds such as para-methylstyrene, meta-ethylstyrene, ortho,para-dimethylstyrene, ortho,para-diethylstyrene, parachlorostyrene,isopropylstyrene, ortho-methylhaving the vinyl radical directlyattached'to a carbon atom of an aromatic nucleus, which compounds mayalso contain one or more alkyl or halogen atoms as nuclear constituents,just described.

The polyethylene glycols suitable for use in preparing the moldingcompositions are relatively long chain glycols, or diols, containing therecurring oxyethylene group (OC2H4) and having an hydroxyl group (OH)attached to the terminal carbon atoms of the oxyethylene chain. Thecompounds may be prepared by reaction of ethylene oxide with water,ethylene glycol, or a lower polyethylene glycol, e. g. diethylene glycolor triethylene glycol, in the presence of an al kaline catalyst and withthe degree of polymerization controlled to form a product having thePolymers varying from viscous liquids to solids are available and areknown to the trade as Carbowax products. The products are usuallyreferred to as having given molecular Weights or average molecularweights. It is to be understood that the products stated to have a givenmolecular weight, e. g. of 600, usually consist of a mixture ofpolyethylene glycols of different molecular weights, some greater than,and some less than, the given molecular weight. In other words, themolecular weight given is that of the mass, as determined by test, andis an average value.

The polyethylene glycols to be used in preparing the new moldingcompositions should have a molecular weight of from 200 to 1200,preferably a molecular weight between 400 and 1000, althoughpolyethylene glycols having somewhat higher average molecular weightsmay be used.

The polyethylene glycols are usually employed in amounts correspondingto from 5 to 10 per cent by weight of the combined weight of the sameand the thermoplastic monovinyl aromatic resin, but an amount of thepolyethylene glycol of from 5 to 8 per cent is preferred. In general,larger proportions of the polyethylene glycols just described tend toexude or bleed from the polymeric compositions and lesser proportions ofthe polyethylene glycols are less efiective, or ineffective,

to cause formation of products of high impact strength and of pleasingnacreous or mother-ob pearl appearance.

In preparing the new compositions it is important that the polyethyleneglycol be incorupon the properties, impact strength, elongation andflexural strength of the molded articles. In this connection, it may bementioned that the new composition are particularly suitable for porateduniformly throughout the thermoplastic 5 the manufacture of articleshaving a nacreous polymer in order to obtain compositions whichappearance, together with good impact strength can be molded to formarticles having improved and elongation by usual injection moldingopimpact strength, elongation and a nacreous aperations. pearance. Thepolyethylene glycol may be in- The following examples illustrate ways incorporated with the polymer, e. g. polystyrene, which the principle ofthe invention has been by mechanically agitating the heat-plastifiedapplied, but are not to be construed as limit- *pDIYiLlZI with thepolyethylene glycol by a rolling the invention.

ing, eading, or extrusion operation, or by dissolving the polyethyleneglycol in monomeric styrene and thereafter polymerizing the styrene Inac o e serles of experiments. e mixture by heating the mixture in bulk,i. e. in the subconsisting of gr r me grade p ystyr n stantial absenceof inert liquid media, in the and a polyethylene glycol having anaverage presence or absence of a polymerization catalyst molecularweight of 600, in the proportions insuch as benzoyl peroxide,di-tertiary-butyl perdicated in the following table was sealed in oxide,or tertiary-butyl hydroperoxide. The vacuum in a closed glass containerand heated compositions may also be prepared by mixing to a temperatureof 200 C. over a period of 2.5 the polyethylene glycol with the granularpolyhours, then cooled. The polymer was melted and mer, e. g.polystyrene, heating the mixture to a the mixture had coalesced to forman opaque temp rature abov t m tin p int o t p solid mass. It wasremoved from the container mer until the mixture coalesces to a homoandcrushed to a granular form. The composiuS Ina-SS d thereafter c o thetions from each of the experiments were injec- In all Such methods the Py y tion molded under a pressure of 9000 pounds per col is preferablyincorporated with the polymer square inch and a temperature as indicatedin in the substantial absence of air or oxygen in th table t f rm t tbars having t i order to reduce the tendency toward deteriorasions I linch x 1 inch X 2 inches These test tion of the heat-plast1fied polymer.The po bars were used to determine the tensile strength ethylene glycoli usually incorporated with the in pounds per Square inch of crossSection the polymer by feedmg mlxture of w granular per cent of itsoriginal length by which each pqlymer and the polyethylene glycol IntoContact product could be elongated under tension before sun-ices of.heated rolls adapted for breakage occurred and the impact strength offi fig g g gfi i g g s fi Y each product in foot-pounds of energy perinch g p n ea 8 arm of notch, applied as a sharp blow to cause breakbyextrusion. An apparatus suitable for incorage of a test bar. Except forthe shape and pora'tmg the polyethylene glycols Wlth a thermo'dimensions of the test bars and the wei ht 0! plastic monovinyl aromaticresin, e. g. poly- 40 the hamme us d t th styrene, is described in U. s.Patent 2,488,189. th 5 e i g f f f f S f Pigments or dyes may also beincorporated with e pmce mes m e ermmmg e e the resinous compositionsstrength and per cent elongation were similar In practice thepolyethylene glycols are tg those descnbed in A. S. T. M. D6 38-44T andtimately incorporated in the desired proportions t e procedure fPnowed mmeasurmg impafzt with a thermoplastic monovinyl aromatic resin Strengthwas slmnar to that described; m by any of the methods just described, i.e. by dis- 1325643'1," other i places solving the polyethylene glycol inthe poly were used to determine the heat distortion temmerizablemonomeric compounds, e. g. styrene, g f f g g ggg gg 22%: and 01 erizinthe mixture in bulk, or b heati g iei mixtu re of the solid resin andtn: I idePtifieS each l on by naming the inpolyethylene glycol in thedesired proportions gredlents of mlxture from Winch it was to aheatipiastif ing temperaturrand ifrechairtiligg ggfeig i zi g i'ginfizgizz g sg ig; cally agi a ing he mix ure. erea er, e solid polymericcomposition is crushed or ground plopeltles determmed f eachcomposltwnto a size suitable for use as a molding powder. F p p of p s pstyr n on The manner in which the polymeric composiand compositionsoutside the scope of the intions are molded to form articles ofmanufacvention are also included in the table as runs 1 ture has anefiect upon the appearance and also 2 and 6, respectively.

Table I Compositions Properties of Compositions Parts Parts T gn i'if i.Impact Per Cent Tensile D g r gzg e511??? g gfi i gg" ElongationStrength ,12%? pp r 100 o 390 1.41 2.6 7,570 81 Transparent.

99 1 380 1. 54 2. 7 7,800 79 Do. 5 350 2.26 12.8 6,320 71 Macreous. 93 7350 1. 92 7.8 4, 700 71 Do. 91 9 350 1. 67 5. 5 4.370 72 Do. so 11 3401.71 5.1 4,180 73 Bleeds.

5 EXAMPLE 2 containers: and crushed toa granular form. Por- A series ofexperiments similar to those. of trons of-each of the compositions weremJection molded to form test bars of A; by A; inch square cross-section.These test bars were used to determine the properties of thecompositions as in ample 1 were carried out, wherein the moldingcompositions were prepared from mixtures con sisting of 95 parts byWeight of granular polysty' Example 1, except that the impact strengthwas remand 5 Parts of a Polyethylene glycol having determined infoot-poundsof energy applied as a an er m lec l r e gh as indicated inthe sharp blow to cause breakage of a test bar. Table ablee tensile smpaSt III identifies the composition by indicating the per cent elongationand heat distortion temperaaverage molecular weight of the polyethyleneglyture of. test bars molded from the compositions col used in preparingthe same. The table also at the temperature stated in the table weredetergives the properties determined for each compomined asin'Example 1. Table II indicates the sition.

Table III Properties of Compositions Run 0 W e of Poly- FY 1 I -gg PerCent f g' tfii f A yce .treng I 'reng ppearance Foot-lbs. Elongutlonlbsjsq. in. 98

0.08 24 6,500 82 Transparent.

3 0.136 7 l 6, 210 Nae-semis. 600 0. 148 9 1 5. 460 72 Do. 1 .600. 0.148 6 9 4.960 7-1 D0. 1.000 0.113 5 9 4, 700- 0 Do.

'lolyethylenc glycol having an average molecular Weight of 600 fromdifiercnt source than polyethylene glycol used in run 3.

average molecular weight of the polyethylene W EXAMPLE 4 y l used nPreparing h Compositions and In each of a series of experiments, amixture also gives the pr p determined o ea consisting of 95 parts byweight of granular composition. molding grade polystyrene and 5 parts ofa poly- Table II Properties of Compositions Average R tt l T H .1)-

un Co. 0 oyemp., Impact Temne ea 1sethylene F. Strength Per Cent tortlongth Appearance Glycol Foombs. Elongation lbs/min" T2161)" 390 1.41 2.67, 570 81 Transparent.

200 350 2.02 6.6 5, 820 69 Nacreous. e00 350 2.26 12.8 6,320 71 Do. 1,200 350 2. 03 a. 3 5, no 73 Do.

EXAMPLE 3 ethylene glycol having an average molecular In each f a Seriesof experiments, a olymerweight as indicated in the following table wasiz tio mixture consisting of 5 per cent by sealed in vacuum in a glasscontainer and heated weight of styrene and 5 per cent of a polyethylto atemperature of 200 C. over a period' of 2 me glycol having an averagemolecular weight 50 hours, then cooled. The polymeric compositions asindicated in the following table, together with from each of the P S Wecru hed to 0.03 per cent of benzoyl peroxide as polymerizaa granular fland molded into test bars 01 tion catalyst, based on the weight of themixture, A y /l inch Square o -Sec o hese test was polymerized byheating the same in a closed r ba s ere use t determine the Properties 0containerinaccordance with the following schedthe Compositions as in a p1, except ha ule of time and temperature conditions: immersimpactstrength was determined as foot-pounds ing the sealed containers for aperiod of hours of energy applied a a sharp blow to cause breakin aliquid bath maintained at a temperature of age of a test bar. Table IVidentifies the compo- 79 C.; 8 hours at C.; and thereafter heatingsition by indicating the average molecular weight for 48 hours in anoven maintained at a tempera- 60 of the polyethylene glycol used inpreparing the ture of 200 C. The polymeric compositions from same andgives the properties determined for each of the experiments were removedfrom the each composition.

Table IV Properties of Products itl tti Run 0 of Poly- Tensile Heat Dis-Per Cent tortion Glycol Strength Strength, Appearance Foot-lbs.Elongatlon lbs/sq. in.

0. 09 2. 7 6, 350 80 Transparent. 0. 205 6. 0 6. 73 Nacreous.

aseaceo Other modes of applying the principle of the invention may beemployed instead of those explained, change being made as regards themethods or compositions herein disclosed, provided the steps oringredients stated by any of the following claims or the equivalent ofsuch steps or ingredients be employed.

We claim:

1. A molding composition comprising as its principal component, a solidthermoplastic monovinyl aromatic resin and, uniformly incorporated withsaid resin, a polyethylene glycol having a molecular weight between 200and 1200 in amount corresponding to from 5 to 10 per cent by weight ofthe combined weight of the polyethylene glycol and the resin.

2. A molding composition comprising as its principal component, a solidthermoplastic monovinyl aromatic resin and, uniformly incorporated withsaid resin, a polyethylene glycol having a molecular weight between 400and 1000 in amount corresponding to from 5 to 8 per cent by weight ofthe combined weight of the polyethylene glycol and the resin.

3. A molding composition comprising solid polystyrene having uniformlyincorporated therewith a polyethylene glycol having a molecular weightbetween 200 and 1200 in amount corresponding to from 5 to 10 per cent byweight of the combined weight of the polyethylene glycol and thepolystyrene.

4. A molding composition comprising solid polystyrene having uniformlyincorporated therewith a polyethylene glycol having a molecular weightbetween 400 and 1000 in amount corresponding to from 5 to 8 per cent byweight of the combined weight of the polyethylene glycol and thepolystyrene.

5. A molding composition comprising solid polystyrene having uniformlyincorporated therewith a polyethylene glycol having an average molecularweight of 600 in amount corresponding to from 5 to 8 per cent by weightof the combined weight of the polyethylene glycol and the polystyrene.

The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Ducca July 11, 1944 Number

1. A MOLDING COMPOSITION COMPRISING AS ITS PRINCIPAL COMPONENT, A SOLIDTHERMOPLASTIC MONOVINYL AROMATIC RESIN AND, UNIFORMLY INCORPORATED WITHSAID RESIN, A POLYETHYLENE GLYCOL HAVING A MOLECULAR WEIGHT BETWEEN 200AND 1200 IN AMOUNT CORRESPONDING TO FROM 5 TO 10 PER CENT BY WEIGHT OFTHE COMBINED WEIGHT OF THE POLYETHYLENE GLYCOL AND THE RESIN.